Keeping The Water Flowing

Just waiting to clog your engine's raw water system.

Just waiting to clog your engine’s raw water system.

Left to my own devices I could happily be a lazy guy, but that’s by no means a good thing to be when you’re in charge of a boat. When running charter boats that are in daily use, daily, weekly and monthly maintenance check lists are absolutely de rigeur to ensure that, random mechanical failure apart, the boat (and most particularly the engine) functions effectively.

There’s no consequential loss insurance available in this regard – blow the engine up through simple carelessness and that’s you out of the game. And it’s even more important when you’re in out of the way places.

So every day I check the oil level, water level, raw water filter strainer and belt tension, and have a good look around under the engine for any signs of leaks or stray nuts and bolts. This simple detective work has saved me endless hours of grief, through nipping many an impending catastrophe in the bud. And every time we start the engine, we check that the exhaust is pumping cooling water – just in case.

With Good Reason

This is especially important in polluted harbours and rivers, where there’s any amount of plastic debris ready and waiting to block your water cooling system.  Some of the harbours here in Brazil are the worst I’ve ever seen for rubbish in the water, Salvador and Rio standing out in particular.  When entering or leaving such places under power we’ll usually have one of us on rubbish watch, and work our way around any particularly bad patches.

We check the raw water strainer daily.

We check the raw water strainer daily.

A few weeks ago during one of my daily checks, I noticed that the level of water in the sea water strainer was lower than usual. This could have been caused by a number of factors, including an air leak at the seal on the strainer, a blockage in the inlet pipe (possibly barnacles or other growth), or a failing raw water impeller. So I stripped the lid from the strainer, cleaned it thoroughly and lubricated the neoprene seal.

Next job was to dive under the hull with a screwdriver and check the inlet pipe was clear (it was). A quick run of the engine indicated some improvement, so we decided to give it a few hours test run before checking the impeller, as it had only 200 hours running time on it.

Think Again

After a few hours running, I checked the water level in the strainer once more, and it still didn’t seem right, so it was time to check the impeller. This has been made easy on Pèlerin by the installation of a Speedseal Easy Slider cover in place of the standard unit. These simple units are essential equipment in my view, and I’ve installed one on every boat I’ve ever owned. Replacing the standard cover with its fiddly (and easily dropped and lost) screws and the vulnerable gasket with four knurled hand screws and an inset O ring means that the cover can be removed, the impeller replaced and the cover back on in minutes, maybe vital minutes – in theory, at least.

The Speedseal cover in place

The Speedseal cover in place

In fact, there’s more to it than that to make the most of this useful item. Any new impeller should have the shaft lubricated at installation to stop it becoming stuck to the shaft, as well as the blades to stop them sticking to the pump body at first start up. Volvo supply a little tube of glycerine to do this with each new impeller, and Speedseal supply tubes of a silicone based lubricant to do the same job. Doing this alone will make life far easier at the next impeller change, and extend the life of the impeller.

Otherwise you’ll be trying to prise out the impeller with all manner of potentially damaging weapons, like a pair of screwdrivers – if the old impeller is stuck on the pump shaft that’s the sort of last resort solution you’ll have to reach for. But, if the impeller was in fact OK, then it certainly won’t be OK any more, and if you damage the soft metal of the pump flange, you may well have problems with leaks in the future. Many years ago I bought a proper Jabsco impeller puller, which has proved invaluable ever since, not just on our boat, but on loan to others. They don’t cost much and are easily available, and you’ll never risk mangling the pump flange or an impeller again.

Buy an impeller puller - worth every penny

Buy an impeller puller – worth every penny

And The Impeller?

In the pump it looked fine, but you really can’t tell until they’re on the bench in front of you for proper examination. Once I could get a good close look, it was clear that the impeller was on its way out. The blades had taken on a permanent curve in the direction of rotation, and there were cracks on at least two of the blades – time for a new one.

Perhaps the amount of time we’ve spent up rivers and in dirty harbours had proved too much for it, as I’ve known these impellers to last for years if looked after and removed and lubricated during winter lay-up. But this experience has convinced me that it’s false economy to keep an impeller in use for longer than a year, and in future we’ll install a new one on an annual basis.

So we dug into the engine spares locker for a new impeller (we always carry at least three spares) and O ring, cleaned the pump face and the Speedseal cover and lubricated the pump shaft and the new impeller.

If you’ve ever struggled with installing a new impeller in this type of pump, this can be made easy by bending the blades into the correct plane of rotation and then tightening a cable tie around them to keep them compressed, then tap the impeller gently into place – done like this it’s simplicity itself. On with the cover, open the seacock , start the engine – result? Perfect – water level correct in the strainer, and a noticeable improvement in pump volume at the exhaust.

Use cable ties to compress the blades to make installation easy

Use cable ties to compress the blades to make installation easy

If a Job’s Easy, You’ll Do It

Far too often we put jobs off because they’re tricky or messy – the old adage that ‘if it ain’t broke, don’t fix it’ always surfaces at such times. But make it simple and quick, and there’s no excuse for inaction, and the simple actions suggested here will make this job a breeze, without breaking the bank. And check, check, and check again!

Enjoyed this article? Please share:

Meet the Author


Colin, European Correspondent here at AAC, is a deeply experienced offshore sailor who holds a Yachtmaster licence, and a gifted photographer and talented writer who has added a whole new dimension to Attainable Adventure Cruising. In addition, since Colin and Louise are from England and had their OVNI 435, Pèlerin built in France, they bring a European perspective to our site. You can read more about Colin and Louise and their business at their website.

Members, login to comment. Not a member? Join Today

82 comments … add one
  • John Apr 6, 2013, 8:37 am

    Hi Colin,

    A post full of really useful information, as always. I really like the wire tie to compress the blades for installation tip. I must have replaced thirty or so impellers over the years, but I have never thought of that.

    • Colin Speedie Apr 6, 2013, 3:09 pm

      Hi John

      I can’t remember where I picked it up – probably somebody trying to stop me turning the air blue as I fiddled with installing an impeller the old fashioned way!

      Best wishes


      • Marc Apr 9, 2013, 5:23 pm

        Funny, I installed a replacement one of those plastic “basket” strainers on my 33 footer just yesterday. I think you’ve finally convinced me to order a couple of Speedseal kits, one for my old Atomic 4 and the other for my new Beta 60 on the steel boat. And an impeller puller; I use a prop puller, and this is basically the same thing, so I don’t know why I’ve put it off.

        The cable tie idea is brilliant. I owe you a pint for that.

        I wonder if, while we are on the topic, you have an opinion on the idea of standpipes that rise above the WL. The boat builder for my steel boat welded one amidship, just offset to one side. There are four one-inch, seacocked T-offs for engine cooling water (it goes to a Perko and then to the raw water pump), one for the head and one to a March pump for use by the A/C unit, plus a spare. The real advantage is that you can physically clear out the pipe from above, and from inside the boat. A previous owner sucked in a fish, noticed the engine temperature was rising, and solved the issue with a broomstick! I am considering a hinged strainer plate to perhaps deter critter and bag ingress, properly insulated from the steel hull, of course.

        I rarely see standpipes on private boats, and I’ve often wondered why. A heavily glassed in version would be as strong as the Schedule 80 pipe from which mine is made.

        • Colin Speedie Apr 9, 2013, 5:37 pm

          Hi Marc

          I think the standpipe/manifold idea is absolutely the best way to handle seacocks there is. And the only builder I’ve seen who does it that way is Boreal.

          With a manifold on stand pipes you can have easy access to the seacocks, and they’re up where they should to remove them if necessary without sinking the boat! What’s not to like? Every builder offering ocean going craft should be considering just this.

          In fairness, I once saw a Rival (many years ago) with a similar installation, but I can’t tell you if it was standard or an owners choice.

          Glad you liked the post – I’ll look forward to the pint!

          Best wishes


        • John Apr 10, 2013, 8:56 am

          Hi Marc and Colin,

          Stand pipes sound like a great idea. However there is one big drawback to be aware of: You don’t want them if you have any intention of keeping the boat in the water in a place where it freezes. The reason being that the water will freeze in the standpipe and blow hole in it, thereby sinking the boat. I have a friend who lost a boat in Norway in just this way.

          As an aside: if you do want to freeze in at all, the through hull fittings need to be custom turned with a slight taper as they go up to the seacock, what an engineer would call “drift”. The result is that a plug of ice is pushed out as it expands. Many Dutch metal boats are so fitted.

          • Colin Speedie Apr 10, 2013, 11:32 am

            Hi John

            Thanks for that very sensible heads-up!

            Best wishes


          • Marc Dacey Apr 10, 2013, 12:54 pm

            Once again, a nugget (bergy bit?) of information that I have NEVER heard elsewhere…and yet seem perfectly obvious to any Canadian…or anyone who has overfilled an ice cube tray.

            The taper idea is great. I have no idea if our standpipe features it. It’s exchanges like this that make this website invaluable, even if overwintering in Norway is not on our bucket list. Heck, it might be one day.

        • Victor Raymond Apr 15, 2013, 12:54 am

          I have four standpipes on my Meta Dalu 47 and I believe this is standard practice for this yard. I will have to check to see if they are tapered or not. Brilliant idea!
          I suppose one could also fill the void with a crushable sacrificial tube that would take up volume when inserted but absorb the ice expansion. Even a length of tubing sealed at both ends would work. Will need lots of signage though as a the brain thaws out.:)

          • John Apr 15, 2013, 7:42 am

            Hi Victor

            Just to clarify, I did not suggest drift in a stand pipe. What I said was that a normal sized though hull with drift will not have problems with freezing.

            I doubt that you could put enough drift in a stand pipe that was long enough to extend above the waterline. Also, if there was even a slight bend in the pipe, there could be issues.

            So my recommendation for boats that will freeze in is no stand pipes, at least until I hear from a credible source who has had stand pipes and has frozen in.

          • Victor Raymond Apr 18, 2013, 9:00 am

            Ok here is the solution. Once you have decided to freeze in then correctly sized closed cell “backer rod” is inserted into the standpipe. Whatever little water not displaced by the backer rod will freeze and squeeze the backer rod. It is very simple and inexpensive and weighs almost nothing. A 100 foot roll is about $15.

          • John Apr 19, 2013, 5:27 pm

            Hi Victor,

            Sounds like a great solution, although I would want to test it with a piece of pipe in a freezer before trusting my boat to it. And don’t forget to take them out in the spring, particularly before flushing the head!

  • Scott Flanders Apr 6, 2013, 10:05 am

    Very well written and illustrated. I have one additional comment. Years ago we had a sea nettle problem in the Chesapeake and were cleaning the sea strainers every other day. The cure was removing the traditional scoop strainers and replacing them with Sen Dure scoop strainers that have 1/8″ holes on 1/8″ centers. In the years since we have had zero issues with debris in the strainers. The strainer for a 3/4″ pipe thru hull is #905 and measures 6 1/4″ x 3″. Centrifugal pumps face the strainer wedge forward and rubber impeller pumps face the strainer heel forward.

    • Colin Speedie Apr 6, 2013, 2:32 pm

      Hi Scott

      I haven’t come across these strainers before, so i’ll be sure to look them up. In fact, we don’t have an external strainer at all, as I’ve seen more problems with them than without! It’s also true that most are bronze and so out of the question for an aluminium hull – plastic versions, maybe, if attached with care.

      Best wishes


      • Chris Apr 11, 2013, 2:21 pm

        Our builder delivers (well did, the economy drove him out of business) a fiberglass 47 footer with a sea trunk (closed standpipe) standard. When when we discussed freezing, it sent me off to research.

        When seawater freezes it seeks to expand in volume by about 9%. If one has a 15cm dia standpipe and if one ignores pressure relief from upward and downward expansion, the ice would seek a diameter of 15.66cm. If we include a 25% safety factor (expansion of 11.25%) the diameter sought would be 15.82cm. This would equate to .41 cm on opposite sides of the standpipe. The transmission cable people have adopted compressible liners to deal with compression from external freezing. Seems to me the converse could be done in this situation — line the standpipe as needed with something that can be compressed more than .5cm. One could even conceive of running a capped off section 0f large hose through the length of the standpipe to reduce the ice expansion to tolerable within the structural limits of the material used and still allowing flow. These ideas are passive.
        One could also actively circulate the water in the standpipe and the probability of freezing drops to near zero. It takes very little motion to keep seawater from freezing because of the freeze dynamics involved.

        The other solution I once heard of was the owner made a thick, temporary piston and pushed it to the bottom of the standpipe and then added non-toxic antifreeze above the piston. But that’s heresy from a gathering of cruisers — a dodgy group at times.

  • Ben Eriksen Apr 6, 2013, 10:11 am

    Yes, thanks — 3 great tips here which I’ve written down on the pre-delivery checklist.

  • Colin Farrar Apr 6, 2013, 10:44 am

    Thanks for the wire tie idea!
    Recently I’ve been able to buy impellers (Jabsco, I believe) that have a female pipe thread in the hub. This allows me to spin on a homemade T handle for pulling the impeller.

    • Colin Speedie Apr 6, 2013, 2:34 pm

      Hi Colin

      That’s a new one on me, but it sounds like a good idea, as does your own solution – anything to avoid getting the screwdrivers out!

      Best wishes


  • Roland Apr 6, 2013, 10:48 am

    Great post.
    Thanks for the tip how to compress the blades.
    When you are replacing the impeller also check the inside of the cover plate for wear. It is not unusual that you see wear. If to deep the pump will not work. You can sand the surface down. As an emergency fix you can use the other side of the cover plate. But important to remember. If the cover plate has signs of wear, it is also likely the other side of the impeller is worn.

    • Colin Speedie Apr 6, 2013, 2:38 pm

      Hi Roland

      Good point, and periodic inspection of the back plate is also a good idea, too.

      I’ve kept the original face plate of the pump (which is virtually unused) and a spare gasket or two for just such an eventuality.

      See also the comments below on the new product from Speed Seal, which sounds like a good idea.

      Best wishes


  • JOHN FORSYTH Apr 6, 2013, 11:03 am

    good article —a little inspective maintenance goes a long way—we had an interesting problem with our impeller that may be of interest—before leaving the boat in storage in Mexico I replaced the salt water pump impeller and then had the bright idea that I would flush the salt water system with vinegar and leave it in the system to remove any salt build-up.
    When we came back the cooling water didn’t seem right—hardly any output at low RPM but OK ouput at high revs !!!???—did the usual inspections including pulling the new impeller which looked just fine—after exhausting all other avenues I replaced the ‘new’ impeller —problems solved —that is when I discovered that leaving the impeller immersed in a vinegar bath for 7 months had significantly softened it —so much that it only pumped sufficient water at high revs — lesson learned—won’t leave vinegar and the impeller together for long periods of time
    s/v MOPION
    Gozzard 36

    • Colin Speedie Apr 6, 2013, 2:41 pm

      Hi John

      Interesting story. When you consider just how much hard work these pumps do, it’s amazing that the impellers stand up so well to so much abuse, but as you discovered, there are limits.

      Yet another reason to inspect and replace such items on a regular basis. After all, they don’t cost much.

      Best wishes


  • Chris Apr 6, 2013, 11:08 am

    While I am disinclined to add equipment to boats, I am looking at installing a rotameter in the raw water supply line downstream of the strainer. These meters have no mechanical parts, don’t restrict flow and because of their vertical scaling are instantly readable. These are old and reliable, robust technology found in the thousands in labs, plants and shipping world wide

    • Colin Speedie Apr 6, 2013, 2:50 pm

      Hi Chris

      I presume your aim is to measure/monitor output? If so, good idea, although like you I’m always loath to over complicate. Otherwise it’s difficult to check by just peering over the side at the exhaust.

      Best wishes


      • Chris Apr 7, 2013, 9:18 am

        Not so much output as throughput. And it’s more about early warning. Our first trip on the ICW in 1980, we consumed ten impellers. Suspended sand in the water played havoc. In each case, the overheat warning sounded before we noticed a diminished flow at the exhaust. Volvo didn’t even offer gauges for our engine in those days. Today’s impellers are more robust, and we have only had one destroyed in 1300 hours, but when it failed the noticeable symptom was fluctuations in the coolant header tank, not exhaust flow. I suspect this is a boat by boat issue.

        • Colin Speedie Apr 7, 2013, 9:31 am

          Hi Chris

          point taken, and I agree that this can be a boat-by-boat issue. The only warning that something was amiss for us was the reduced level in the water strainer, which could easily have been caused by a number of faults, hence the forensic check. But I had seen something like this before, so knew that impeller might be the culprit.

          And as for alarms, the ones Volvo installed on our engine are all but inaudible, so we’re going to try and locate LOUD ones whilst ashore later this year – what’s the point of alarms if you can’t hear them?

          Best wishes


          • Chris Apr 7, 2013, 9:36 am

            Colin, you might want to give the automobile security suppliers a look.

  • Martin Apr 6, 2013, 11:28 am

    Very nice article with good practical tips. Regarding the Speed Seal product, I looked it up and there seems to be two products – the Easy Slider (mentioned above) but also something called “Speed Seal Life”. Incredibly, the latter claims to protect the impeller when run dry for as long as 10 minutes (and adds 300% to its normal life).
    It seems to protect the outsideside edge of the impeller from heat friction (PFTE disc), but I would have thought dry running damages the fins as they are squashed against the cam, and the pfte disc does nothing to stop this friction/heat. So any experience or insights from readers about this dry running claim would be appreciated.

  • Robin Atkinson Apr 6, 2013, 12:50 pm

    The principal wear occurs between the impeller face and the face plate, allowing the water an easier alternative path. The new arrangement has an indentation in the face plate, in which two discs (one PTFE), spin freely with the impeller, eliminating wear in this critical area.

    • Colin Speedie Apr 6, 2013, 2:55 pm

      Hi Martin and Robin

      I wasn’t aware of this new product, but I certainly like the look of it, and as I can see that there’s an upgrade kit for existing Speed Seal installations we may well purchase one.

      Another interesting option might be to look at one of the run dry impellers (e.g. Globe Run-Dry) available in the US, as an additional advantage.

      Best wishes


    • Martin Apr 6, 2013, 8:52 pm

      Take your point about principal wear point, Robin, but do you mind explaining why there is not even more friction where the fins rub against and are bent backwards by the cam?

  • John Rushworth Apr 6, 2013, 12:59 pm

    Makes me glad I have electric propulsion 😉

    • Colin Speedie Apr 6, 2013, 2:57 pm

      Hi John

      Quite – but don’t you get bored with nothing to service?

      Best wishes


      • John Rushworth Apr 6, 2013, 3:02 pm

        It has taken me a year to refit as you can see so there is no time to be bored! Hope to launch in the next 3 weeks after the surveyor has been. She will be the first MCA coded electric propulsion sailing yacht in the UK to MGN 280 standards for “Small Commercial Vessel and Pilot Boat (SCV) Code” . Coding to CAT 2 up to 60m and the stability came out better than many boats 10’ft longer, so pretty chuffed and looking forward to zero ‘engine’ maintenance!

        • Colin Speedie Apr 6, 2013, 3:07 pm

          Hi John

          Looks great, and I’ll be really interested to hear how everything works out in practice, especially if you’re going to work her, which in my view will give a really good overview of how such conversions go in the real world.

          Best wishes


          • John Rushworth Apr 6, 2013, 3:09 pm

            Thanks Colin. We shall see. Mostly shake down this year and see how it goes around the Clyde and west Coast. Will keep you posted or simply like my Facebook public page.

  • Dan Apr 6, 2013, 2:39 pm

    Your debris field photo looks like the mess between our boat and dock in Charleston. Nice raw water filter too. Every time we return to Charleston to visit Halcyon, it’s that raw water start up fear. I’d love to redo whole raw water system and make it favor serviceability. How about the through hull having a Y for clean out via high pressure water or wire brush. My pain is the oh so sensitive refrigeration intake. Just a little film keeps the noisy compressor running. I just found out about keel coolers. It just seems like very few designers if any take the time to make it easy. Aren’t these maters inevitable? I’m always to dive bellow, I just want it to be for that thing we didn’t see coming.

    • Colin Speedie Apr 6, 2013, 3:03 pm

      Hi Dan

      That’s in Rio after a thunderstorm – I’ve never seen so much rubbish.

      The raw water filter is a Vetus product, and very good it is too. A good idea with any of these filters, though, is to check the condition of the large O ring that seals the lid on a regular basis, clean it carefully, and the land it sist in and then sparingly lubricate the O ring with a silicone type grease. Otherwise salt and contaminants can build up and cause air leaks and reduce the life of the O ring.

      One thing I have seen is a divertable Y valve leading to two of these filters, in case one blocks, but the owner did admit he’d never had cause to use it.

      And don’t get me started on designers…..

      Best wishes


  • paul Apr 6, 2013, 2:58 pm


    Any chance we could convince you to post an article on your daily, weekly, monthly, annual maintenance items. It would be great to get this perspective from seasoned veterans!

    Thanks for another great article.

    • Colin Speedie Apr 6, 2013, 3:12 pm

      Hi Paul

      I’ll do my best – good idea.

      Glad you like it!

      Best wishes


  • Collin Harty Apr 6, 2013, 3:20 pm

    We once had an impeller disintegrate on a boat we chartered on the east coast of Australia. It took three engine overheatings and three trips back to the charter base before they successfully cleared all the deprise from the cooling system. One simple idea I’ve incorporated on my boat, to avoid this problem in the future, is to install a strainer downstream of the rawwater pump in case the worst happens. Experience can be an annoying, if not persistent teacher.

    • Colin Speedie Apr 6, 2013, 3:30 pm

      Hi Collin

      Excellent point, and another reason for periodically checking and/or replacing the impeller. I had this happen once on a previous boat where the intake got blocked with a plastic bag, and the impeller just exploded. We spent many happy moments clearing bits of it out of the heat exchanger core….

      Best wishes


  • Matt Marsh Apr 6, 2013, 5:22 pm

    A question for any engine manufacturers out there: Why are we still using flexible impeller pumps for this?

    They self-destruct if they’re run dry, suck up debris, get too hot, get too cold, or are left on their own for extended periods. The last time I had one lose a vane on me, one of the fragments lodged in the cylinder head, causing the head gasket to blow. (Cylinder full of raw water = good-bye outboard motor.)

    Is there any reason why a different pump type (a radial-flow centrifugal, for example, which can run dry, can self-prime as long as there’s any water at all in the housing, can be made extremely hard to clog, and takes >10,000 hours to war out) isn’t used instead?

    • Colin Speedie Apr 6, 2013, 7:03 pm

      Hi Matt

      Good question indeed.

      I asked myself something similar in a chandlery recently whilst overhearing a conversation involving a guy trying to obtain a replacement impeller for an outboard. It would seem that there’s absolutely no standard impeller – every engine seems to have a different one, even between similar models, which makes getting the right one a real pain.

      But look at the price of the replacement (if and when you can get it)!

      I remember from my motorcycling days being told that the Japanese manufacturers made more money on spares than they did on the bikes – maybe that’s at least part of the reason?

      Best wishes


    • Douglas Pohl Apr 6, 2013, 9:20 pm

      Excellent alternative pump idea and while you are at it why not upgrade to an external keel cooler (i.e. no raw sea water nor debris will ever enter your machinery cooling system because its closed loop. I’ve been using the above mentioned mfg keel coolers on three previous boats over 25 years with excellent results – no business interest – just a very satisfied customer.

  • Danny Blake Apr 6, 2013, 6:27 pm

    Hi Colin
    Have been reading the website for a few years now,and at last I think I have something to add, I own a single engine motorboat in Guernsey C.I. when fitting it out I search for something that would give me early warning of a blockage on the incoming raw water, and came up with a vacuum switch and buzzer, just needed to tap a 1/8 hose barb into the strainer body, then attach 2″ of clear hose wrapped into coils, attach this to the vacuum switch, wire up to buzzer then adjust vacuum switch for sensitivity required, all in cost about £25 and 5 hours work, not a bad early warning at a great cost.
    will send photos if of any interest to anybody. keep up a great site thanks for a great resource.

    • Colin Speedie Apr 6, 2013, 7:06 pm

      Hi Danny

      Well it was worth the wait!

      Sounds like a great idea, especially as by the time a temperature sensed alarm goes off, all too often the engine is cooked already.

      Best wishes


  • pat Apr 6, 2013, 8:57 pm

    Like Danny I have a simple and inexpensive early warning. I’ve fitted a temperature alarm in the exhaust system. This heats up much faster than the motor if the cooling water slows or stops.
    My Murphy switch gages are still “as good as new” after 25 years. A good investment.

    • Colin Speedie Apr 7, 2013, 6:48 am

      Hi Pat

      Again, a good option. When we haul out later this year we hope to make a number of modifications to Pelerin while we’re not living aboard, and installing some form of temperature warning system is amongst them – and it would seem from what I’ve read that many of the best components come from the US.

      Thanks for the useful advice.


  • Richard Wuilliam Lord Apr 6, 2013, 9:42 pm

    Food for thought:

    If a car engine doesn’t have / need an impellor, why does a boat..?? What’s the difference..??

    • Colin Speedie Apr 7, 2013, 6:52 am

      Hi Richard

      There are options – see Douglas’s sensible suggestion above. Cost and conservatism might be the main reason for the lack of innovation in this field. And with the increasing demand for alternatives to fossil fuel, at some stage in the not too distant future we may not have to worry about this…

      Best wishes


    • Matt Marsh Apr 7, 2013, 9:26 am

      Car engines usually have a centrifugal pump with a rigid, metal impeller. You don’t notice it because it almost never fails- it just gets replaced every 100,000 km or so when you change the timing belt, and even then it can usually be refurbished and used for another 100,000 km.

      Worrying about a water pump is something we should have outgrown 50 or 60 years ago. They’re not complicated, and even in the 1940s we knew how to design pumps that would never fail.

  • Robert Reyes Apr 7, 2013, 8:18 am

    Thank you for these tips. Now if we can just get Yanmar to put the pump where it is accessible ; on my three cylinder it is hidden between the alternator and starter motor facing aft !!!.

    And by the way, don’t use vinegar solutions to deodorize your head. I had to replace all rubber gaskets after I followed the recommendation of a well meaning friend.


    • Colin Speedie Apr 7, 2013, 9:19 am

      Hi Robert

      I know – why do they do these things? If you combined the engine inaccessibility of our Ovni with a Yanmar engine with the same configuration as yours, even Houdini couldn’t change the impeller.

      However, in your case I hope the little tweak with the cable ties helps!

      Best wishes


    • Chris Apr 7, 2013, 9:33 am

      Robert, it is material dependent.
      Glacial Acetic Acid is 100% (no water). White Vinegar is 5-8% so the following table is the absolute worst case.

      Rubber Materials Compatibility with Acetic Acid, Glacial
      1=Poor 2= Fair 3= Somethimes OK 4 = Fully compatible

      Aflas 1
      Buna-N Nitrile 1
      Butyl 4
      Chemraz 3
      Epichlorohydrin 1
      Ethylene-Propylene 4
      Fluorocarbon 1
      Fluorosilicone 1
      Hypalon 2
      Kalrez 4
      Natural Rubber 1
      Neoprene 3
      Nitrile, Hydrogenated 3
      Polyacrylate 1
      Polysulfide 3
      Polyurethane, Cast 4
      Polyurethane, Millable 1
      Silicone 4
      Styrene Butadiene 3
      Teflon, Virgin 4
      Vamac 1

  • Dick Stevenson Apr 7, 2013, 4:17 pm

    Colin, I second Pat’s suggestion of a exhaust hose high temperature alarm and one can look to for the alarms in the US. Engine high temp alarms can be a concern because of the fine line between the alarm going off and damage occurring, sometimes serious damage. I have also used Speedseal for decades. The company is a delight to deal with and Alex sent a new cover without charge when mine started to look worn. With regard to impeller driven pumps and their deficiencies, I know of at least one cruiser who spliced in a spare water pump when his original pump packed it in and he had no spares and went merrily on his way for 100s of engine hours. My admittedly makeshift genset has a Flojet fresh water system pump (no pressure switch) for a raw water pump and it has 800+ hours on it.
    Dick Stevenson, s/v Alchemy

    • Colin Speedie Apr 7, 2013, 5:04 pm

      Hi Dick

      That looks like a very good option, and I totally concur that the standard engine alarm is usually way too late. I, too found the Speedseal guys always to be very helpful, and I’m impressed that for their new product they are offering an upgrade for existing customers, so that you don’t have to but the whole thing again – good for them.

      And I saw a similar fix to the one you mention in French magazine Voile et Voiliers recently, where a yacht crossing the Atlantic had the shaft shear on their raw water pump, and they just plumbed in spare domestic water pump. They made it across safely, which just goes to show what you can achieve with a little ingenuity!

      Best wishes


      • Chris Apr 7, 2013, 5:37 pm

        A few years back, the raw water pump on our genset self destructed. After looking at our options, I put a permanent plate over the face and wired and plumbed in a sealed, magnetically coupled AC vane pump. No more possibility of flooding the diesel with seawater — pump doesn’t come on until genset is putting out 120vac — within 3-4 seconds. We have given a lot of thought to doing this with the main engine using a 12vdc vane pump. These pumps aren’t self-priming, but proper placement takes care of that.

        • Mike Feb 5, 2014, 11:02 am

          I installed a 12 VDC centrifugal sea water pump on my 35 HP Suzie diesel engine in our 30′ trawler. Jabsco 50840-0012 stainless steel pump that delivers 5.3 GPM at 7.4 PSI head. The original engine sea water pump was inaccessible, and it was impossible to properly adjust belt tension the way it was installed. The electric sea water pump has been working fine for the past two years since I installed it.

          I also installed an Aqualarm flow sensor and alarm.

          I kept the old belt-driven sea water pump installed on the engine for emergency back-up use (without the belt ). I installed tees in the suction and discharge hoses so that the old sea water pump can be hooked up with minimal effort – just install the belt, listen to the squeal since it can’t be adjusted properly, and off we go.

    • Alan Apr 7, 2013, 9:48 pm

      Re exhaust temp alarms there is also this new product from NASA Instruments,
      it should have a faster response time than the Borel unit (which I had been considering because it is directly measuring the exhaust water/gas temp.
      On the water side there are various flow switch alarms such as and I believe Groco has something similar.
      In relation to the queries about using rubber impeller pumps, these are for sure a compromise but apart from having to often provide a bit more head than a typical cooling water circulation pump, they also have to able to survive pumping water that, even with filters, is not exactly clean.

      • Colin Speedie Apr 8, 2013, 6:26 am

        Hi Alan

        Interesting new option from NASA, at an attractive price. For what it’s worth, I’ve had quite a few items from them over the years, and while I thought in the early days it was bit cheap looking, finish and reliability seemed to improve with time. Certainly our wind instruments lasted as long (or longer) than some ‘name’ brands with much larger price tags.

        Thanks for that


  • Dave Benjamin Apr 8, 2013, 12:12 am

    Excellent article. Couple other suggestions:

    1. If the raw water inlet is closed for the strainer service, it’s a good idea to attach the engine key to the handle. This prevents starting the engine with the valve still closed.

    2. We’ve found some O-rings supplied with the impellers that are supposed to fit our 75hp Yanmar turbodiesel don’t fit it well. So now we make sure we have that Yanmar supplied O-ring. In order to install the ill fitting O-ring, we discovered that heating it in very warm water prior to install provided a good fit.

    3. I’m planning to install one of these raw water alarms. I know the owner of the company and have heard good things about it. If anyone has used one, perhaps they can share their thoughts.

    • Colin Speedie Apr 8, 2013, 6:37 am

      Hi Dave

      Good point on the key idea – we don’t have keys for our Volvo engine, but I do always leave an A4 piece of paper on the chart table when we leave the boat with ALL SEACOCKS CLOSED on it, so that the biggest fool on the boat will remember to open them all on return. No doubt like you I’ve seen the
      inevitable happen otherwise, with expensive consequences.

      I hate to say it (due to the cost implications) but often times you’re safer with spares from the manufacturer due to the poor fit of some replacements from after market firms. Not all, just some, and it’s poor economy on occasion. Filters, O rings, gaskets etc, I only tend to buy from known brands.

      And yours is the second mention here for the Borel alarm, which looks like a good unit, and at a good price. 103dB too, so that should let you know something is going wrong!

      Best wishes


      • John Rushworth Apr 8, 2013, 6:47 am

        And for a bit of levity. Due to electric propulsion I leave a note on the chart table by the key, saying “No Seacocks” 😉

        • Colin Speedie Apr 8, 2013, 6:54 am

          Hi John

          Love it – but don’t rub it in…..

          Makes you think though – another thing you don’t have to worry about with electric propulsion.

          Best wishes


          • John Rushworth Apr 8, 2013, 8:08 am

            🙂 The reality though is pure electric propulsion is never going to be close to hull speed for any duration and the punching into weather solution that John needs. My criteria was to replace an auxialliary propulsion diesel for something simpler with a back up hand portable small Honda generator that gives me 3 kts @ 1/2 litre petrol per hour (I can only carry 5 litres for coding safety purposes) without using any battery. I could use a bigger generator but that would mean a bigger more expensive charger too than the 600 Watt 24V/25Amp Victron one I have. Also access to my PSS seal with the old diesel was all but non existent in an emergency with the tight space on a 26ft double ended boat. Another reason to simplify and gain space. And one of the best reasons is I’m getting older, less flexible and do not have facilities or cash to rebuild a diesel myself these days. With the exception of my batteries everything about my conversion has been hand carried to the boatyard in a small Musto shoulder bag. My point is I hope to have ease and simplicity and learn to sail better. In fact, I’ll have to as there is not the reserve of power or fuel that you can get with a pure diesel.

        • John Apr 8, 2013, 4:11 pm

          Hi John,

          Sounds to me like a fun, interesting and worthwhile project, that you went into with realistic expectations Please keep us up to date with how it works out.

  • Steve A Apr 8, 2013, 12:28 am

    I have been using the blue Globe “run dry” impellers for about 15 years. I had a commercial boat that had been converted to a keel cooler & dry exhaust. The old Jabsco raw water pump was used to supply constant raw water on deck for fish cleaning. I had to shut off the thru hull intake one extremely cold winter, and assumed I would need to replace the impeller in the spring. About 30 HOURS of running later I opened the thru hull and the water flow was fine. I used the same impeller all that summer season (800 hours?) and shut the thru hull the next winter and again ran it dry. The next spring the flow was down to a trickle, but probably still better than a standard impeller run dry for 10 minutes. The last Globe impellers I bought were thru Defender.
    AquaAlarm has an inexpensive adjustable water flow alarm kit for $100-$150 if I remember correctly. Just adjust it so the alarm does not go off while you are at idle. A much earlier warning of flow problems than an over heat alarm.
    Groco sells a nice bronze dual sea strainer. I think that set me back at least $1,000, peace of mind can be expensive!

    • Colin Speedie Apr 8, 2013, 6:49 am

      Hi Steve

      Thanks for the real world experience with the Globe impeller – must get one!

      We’ve always intended to install an additional temperature alarm, for all of the reasons outlines in the great comments we’ve received on this post, so we’ll be doing some planning before we lift Pelerin out later this year. Once we’ve installed and tested our selection we’ll let you all know how it works out in practice.

      Best wishes


  • Alan Apr 8, 2013, 4:33 pm

    Colin, as a follow up to your recommending the Jabsco Impellor puller, if the installation does not have the space to use one (I have this problem with a fridge compressor obstructing access), one of these long nose pliers is a very good alternative, such as
    most tool manufacturers produce something similar

  • Colin Speedie Apr 8, 2013, 8:13 pm

    Hi Alan

    Yes, those would do the job well – as well as many others. I have an old pair of circlip pliers aboard that are handy for similar non-destructive tasks, but fortunately for us there’s just enough room to get the puller into place.

    A good set of pliers are well worth carrying, so thanks for pointing this out.

    Best wishes

    C olin

  • Steve A Apr 11, 2013, 12:40 pm

    Hi John,
    Thank you for the post on the need for stand pipe “drift” or taper to allow ice movement to prevent expansion splitting the pipe. I’m surprised this detail was not mentioned in a book I have that discusses stand pipes. I expect the Adventure 40 will have many such unseen details addressed that are due to attention to detail and many years of experience.

    • John Apr 11, 2013, 3:05 pm

      Hi Steve,

      Just to clarify, I did not suggest drift in a stand pipe. What I said was that a normal sized though hull with drift will not have problems with freezing.

      I doubt that you could put enough drift in a stand pipe that was long enough to extend above the waterline. Also, if there was even a slight bend in the pipe, there could be issues.

      So my recommendation for boats that will freeze in is no stand pipes, at least until I hear from a credible source who has had stand pipes and has frozen in.

      • Marc Dacey Apr 11, 2013, 7:26 pm

        Point taken, John, on the danger of frozen standpipes, but I can think of several methods to keep them unfrozen, including heater wire around the pipe, a handful of salt down the standpipe, a baby bubbler immersed down the pipe, hot air diverted from the engine bay, and a few other methods. All you need do is to keep the ice from freezing and expanding inside the pipe: you could poke “the plug” clear once a watch.

        That said, it’s very much a new cautionary element in what I had thought was a manifest improvement on the average below the WL seacock (which I assume could also freeze under severe enough conditions), and for that, I thank you.

        • Colin Speedie Apr 12, 2013, 7:39 am

          Hi Marc

          I still think that stand pipes are a major improvement in many ways – safety, ease of service etc.

          But John’s cautionary point is one that’s well worth knowing – which is what makes the discourse on this site so valuable to all of us – including yours truly.

          Best wishes


          • John Apr 12, 2013, 9:48 am

            Hi Colin,

            Isn’t always the way in this game: Even an idea like stand pipes that’s 90% good has a drawback!

        • John Apr 12, 2013, 9:02 am

          Hi Marc,
          I agree that there are many ways to stop a stand pipe from freezing or to absorb the expansion if it does (see Chris’ comment above) but all of them are prone to possible failure and add complication. And they only have to fail once. For example, I would never trust the safety of my boat to any sort of heating system. In fact that’s what happened to my Norwegian friend: the heating system failed, a plug of ice cracked the plumbing, and down she went.

          Bottom line, all of these options add complication. Better in my view to just not have them if you are going to freeze in.

          • Chris Apr 12, 2013, 12:18 pm

            The USCG requirement for standpipes in machinery spaces is Schedule 80.

            XS Schedule 80 15 cm dia has a burst strength of 6510 psi. — XXS is 13035 psi.

            Ice formation can generate pressures of 14000 psi at 0C and 40000 psi at -22C

            As you say, if you are freezing in, standpipes are a bad idea — unless one can design them to eliminate the water or ameliorate the pressure (as mentioned before). Then again, the idea of freezing in just isn’t all that attractive either.

          • John Apr 12, 2013, 1:25 pm

            Thanks, Chris. So nice to have the real engineering knowledge around to back up the gut feel. 14,000 to 40,000 PSI, yikes, who knew!

          • Chris Apr 12, 2013, 6:28 pm

            It’s 78F out and blowing 25 kts, the cloud bottoms are turquoise, and while I’m wondering about which rum to use in the Dark & Stormies tonight, I’m having freeze anxiety. What about horizontal standpipes — aka bow thruster tubes? For a truly beset boat, these are going to be a critical failure point.

            Most of these tubes are at least partially in the freeze zone even in more temperate waters. Perhaps the pressure relief out the ends of the tubes keeps the radial pressures from ever reaching critical — unless the freezing starts at the ends and proceeds inward. Hmmmm…
            I think the Goslings…

  • Marc Dacey Apr 12, 2013, 2:47 pm

    I’d have to say that while this is academic (in a good way, however) for us as we would not choose to freeze up in a fjord, it does illustrate once again that man’s ingenuity when it comes to nature is at best going to end in a draw. Something that Shackleton and other polar explorers in wood-plank ships learned the hard way about the properties of ice.

    And now, speaking of which, I have to go down to the shores of Lake Ontario and see if today’s 50 knot ice squalls have shredded my tarps and sent my deck gear into the drink!

  • Steve A Apr 13, 2013, 1:00 am

    Where I live usually only an inch or 2 of ice forms on the surface, and my thru hulls are several feet below that in “warmer” water. My freezing problems have been a foot above the thru hull where cold air can surround the hose. Maybe a piece of hose could be slipped over a standpipe and clamped on as low as possible, extending up above the water line. If the pipe froze and burst this may contain it. Pipe insulation seems to help also.
    Great information on the psi & compressible liners.

Only logged in members may comment:

Leave a Comment

Please read our comment guidelines CLICK HERE